Among the most effective of weight training, or “strength”, machines are those which employ a stack of modular blocks or plates which a user may manually set within a range of weight. The weight stack is typically formed by a stack of rectangular, brick-shaped weight blocks, stacked vertically, wherein one or more rods may be slideably disposed within a vertical channel formed within the stack by a set of vertically aligned holes in each weight block. An additional lifting post is usually disposed in another such channel, typically in the center of the weight stack, such lifting post being further coupled to an assembly of cables and pulleys for actuation by the user. Each block further has at least one horizontal channel or hole, wherein a pin may be disposed to slideably engage any of a series of horizontal channels which are vertically oriented on the lifting post in a spaced apart manner to match the vertical spacing of the stacked weight blocks. The pin thereby engages a portion of the stack of weight blocks, such that when vertical force is applied to the lifting post, the selected stack of weight blocks is moved upwards to create a resistance for use in weight or strength training. Typically, the weight stack apparatus is oriented such that the further down the pin is entered into the lifting post, the greater the number of weight blocks are engaged, thereby increasing the resistance of the machine for use in weight training.
However, effective strength training requires that the weight resistance be selectable to a relatively high degree of resolution. The initial baseline resolution of the weight stack is equal to the weight of an individual weight block, i.e., the resistance may only be varied in increments equal to the weight of an individual weight block. Thus, to increase resolution, the individual weight blocks must be lighter. However, if the aggregate weight of the stack is to be high enough to provide adequate resistance for heavy weight training, and the apparatus is to be compact, the weight blocks cannot be too light. The other option would be to increase the number of blocks in each stack, but design and manufacturing considerations dictate that the number of parts in any apparatus be minimized.
To increase the weight resistance resolution, while providing a sufficiently compact and heavy weight stack, with a minimum number of parts, several different devices and mechanisms have been employed. One involves the placement of incremental weights, having a weight smaller than one of the weight blocks in the stack, directed onto, or in fixed connection with, a portion of the weight stack. The incremental weight may be placed directly on top of the weight stack. Or it may be attached to a portion of the pin extruding from the weight stack. However these options require that additional parts be utilized with the apparatus. These parts may be lost, or may be dropped to cause injury. Furthermore, the incremental weights may shift the center of gravity of the weight stack or otherwise disrupt the balance and weight distribution of the stack around the guiding rods. Another problem is that the incremental weight causes components of the apparatus to bend, thereby placing undesired stress, strain, and torque on the tightly interconnected moving parts, leading to decreased machine safety, efficiency and performance. Finally, in order to increase the safety of such devices, it is usually desirable to provide a weight stack apparatus that is fully enclosed, such that bodies cannot enter the spaces and junctions between the weight blocks and rods during operation.
Therefore, it is desirable to provide for a system of incremental weights which may be employed in a conventional weight stack type exercise machine, whereby the incremental weights do not disrupt the balance of the machine, do not require the use of additional detachable parts, and may be safely enclosed within a covering structure.